Add test for platform encoders, turn off platform encoders by default

src/images/SkForceLinking.cpp

Index: src/images/SkForceLinking.cpp
diff --git a/src/images/SkForceLinking.cpp b/src/images/SkForceLinking.cpp
index 2afe7192a9e3a05661973deb18939881052bae99..81d485c882fef80dfa1227e2eb5273579226a71d 100644
--- a/src/images/SkForceLinking.cpp
+++ b/src/images/SkForceLinking.cpp
@@ -14,28 +14,26 @@
 int SkForceLinking(bool doNotPassTrue) {
     if (doNotPassTrue) {
         SkASSERT(false);
-#if !defined(SK_BUILD_FOR_MAC) && !defined(SK_BUILD_FOR_WIN) && !defined(SK_BUILD_FOR_IOS) && \
-    defined(SK_HAS_JPEG_LIBRARY)
+#if defined(SK_HAS_JPEG_LIBRARY) && !defined(SK_USE_CG_ENCODER) && !defined(SK_USE_WIC_ENCODER)
         CreateJPEGImageEncoder();
 #endif
-#if defined(SK_HAS_WEBP_LIBRARY)
+#if defined(SK_HAS_WEBP_LIBRARY) && !defined(SK_USE_CG_ENCODER) && !defined(SK_USE_WIC_ENCODER)
         CreateWEBPImageEncoder();
 #endif
+#if defined(SK_HAS_PNG_LIBRARY) && !defined(SK_USE_CG_ENCODER) && !defined(SK_USE_WIC_ENCODER)
+        CreatePNGImageEncoder();
+#endif
 
         // Only link hardware texture codecs on platforms that build them. See images.gyp
 #ifndef SK_BUILD_FOR_ANDROID_FRAMEWORK
         CreateKTXImageEncoder();
 #endif
 
-#if !defined(SK_BUILD_FOR_MAC) && !defined(SK_BUILD_FOR_WIN) && !defined(SK_BUILD_FOR_IOS) && \
-    defined(SK_HAS_PNG_LIBRARY)
-        CreatePNGImageEncoder();
-#endif
-#if defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_IOS)
-        CreatePNGImageEncoder_CG();
+#if defined (SK_USE_CG_ENCODER)
+        CreateImageEncoder_CG(SkImageEncoder::kPNG_Type);
 #endif
-#if defined(SK_BUILD_FOR_WIN)
-        CreateImageEncoder_WIC();
+#if defined (SK_USE_WIC_ENCODER)
+        CreateImageEncoder_WIC(SkImageEncoder::kPNG_Type);
 #endif
         return -1;
     }